A conventional electrophotographic apparatus of the above type is shown in Japanese Patent Kokoku Publication No. 54,392/1983. In this apparatus, in an electrophotographic copier, a photosensitive drum and a developing device for toner development of the electrostatic latent image formed on the photosensitive drum in correspondence with the image of the original, and a cleaner for removing any powder developing agent remaining on the photosensitive drum are integrally mounted on a support member, and this support member is slid with respect to the main body of the electrophotographic copier in the direction of the axis of the photosensitive drum for removal and mounting.
The expression "integrally mounted" as used herein means that the named components can be separately disassembled from the rest of the printing apparatus without being separated or disassembled from each other.
In the apparatus disclosed in the above publication, as set forth in the fourth column, the developing device, the photosensitive drum and the cleaner are integrated into a single exchangeable unit, and when either of them reaches the limit of life span, the entire exchangeable unit is exchanged for a new one.
Further, as described in column 6 and column 11, and shown in FIG. 2 in the publication, a toner bottle 20 is provided in the developing device A, and a powder developing agent formed by mixing the toner and the carrier is contained therein.
When the powder developing agent is exhausted, the exchangeable unit as a whole is at the limit of life span, and must be replaced regardless of the consumption or wear of other components. This leads to increase in the printing cost, and is detrimental to the economy of the user. The deficiency can be eliminated by increasing the capacity of the toner bottle, or by lowering the cost of the exchangeable unit. The former measure increases the size of the exchangeable unit, and the latter measure is technically difficult.
Of the components of the exchangeable unit, the toner bottle reaches the limit of life span when the powder developing agent contained therein is exhausted, but, at that time, other components may not have reached their limit of live span, and their limit of life span is dependent on factors other than the consumption of the powder developing agent, for instance the number of sheets that have been printed, and it is practically impossible to have the limit of life span of the toner bottle and all other components to reach simultaneously under various conditions.
For this reason, the user of the apparatus must dispose the exchangeable unit, part of which can still be used, and this is uneconomical to the user.